The most widely used element to protect an individual's hand during work or other endeavors would be a glove. Historically, gloves were produced utilizing a large number of different processes as well as various sorts of materials depending on the variety of applications.
For example, gloves used in gardening and in sports which would require the use of a heavy duty material would be made by sewing pieces of these materials together. These materials would include, but are not limited to leather, fabric, non-woven cloth and various combinations of these materials. Furthermore, these types of gloves were made to last through a number of repetitive usages. Additionally, the purpose of these types of gloves was to protect the user's hand and not necessarily other individuals.
Single use disposable gloves have been produced for utilization in, but not limited to medical procedures as well as for use in the food service industry. These types of single use gloves are employed to protect both the user as well as other individuals from contact with various germs or pathogens. Generally, these types of single use disposable gloves are manufactured using a dipping method or a cutting and heat sealing method.
The dipping method would employ a three dimensional hand shaped former which is introduced into a forming liquid compound. A portion of the forming liquid compound would adhere to the hand shaped former to produce a thin layer of film thereon. After this thin layer of film solidifies, the thin layer film would be stripped from the former, thereby producing a glove. This type of process is generally utilized to produce medical examination and surgical gloves, due to the fact that the combination of the three dimensional former would yield a glove which is relatively form fitting on the user's hand. This is due in part to the effective elasticity of the materials used during the dipping process. This form fitting characteristic of gloves produced by the dipping process is measured by applying stress to the glove for the purpose of deforming the glove and then releasing the glove from the stress. A measurement is then made as to whether the glove fully recovered to its original shape after being released from the stress. For example, utilizing a rubber glove formed from the dipping process, the deformation after a 100% stretch is less than 10%.
The dipping process employs a wide range of plastic and rubber polymers such as, but not limited to, natural rubber latex (NRL), carboxylated acrylonitrile butadiene copolymer (Nitrile), polyisoprene (PI), polychloroporene (Neoprene), polyurethane (PU), polyvinyl chloride (PVC) etc. as well as the various combinations produced via blending and copolymerization of these materials. A combination of these materials can be used from a blend of two or more of these compounds in a single dipping step. Conversely, a multiple dipping process producing a structured film provided with multiple layers can be employed. Generally, medical gloves produced by the dipping process would have a thickness of at least 0.08 mm for natural rubber latex or at least 0.05 mm for the aforementioned compounds. This parameter is required by the FDA and/or ASTM. Additionally, it is noted that it would be extremely difficult, if not impossible, to use the dipping process to produce films having a thickness of less than 0.05 mm without compromising the integrity of the produced film. Among the aforementioned materials, NRL, Nitrile and PVC would account for at least 95% of all commercially produced medical examination gloves. Table 1 lists the major attributes of these gloves.
TABLE 1Typical properties of dipped PVC, NRL andNitrile medical examination glovesPropertiesPVCNRLNitrileTensile Strength (MPA)11~1518~2520~40Elongation (%)300~400~800 ~600Deformation after 8~16~5 5~10100% stretch (%)Thickness range (mm)0.06~0.100.08~0.120.06~0.12Weight (grams)>5>5 >4
While the physical properties of these gloves are quite different in terms of tensile strength and elongation, they also share quite some common characteristics such as thickness, weight, and deformation; after all, the application is the same, for medical examination.
Due to the fact that the combination of the three dimensional former and the minimal deformation, all these materials could yield very good form fitting articles. To characterize the form fitting parameter, a specimen is stressed to deform the article and is then the form is released to measure if the article could fully recover to its original shape. Quantitatively, the dumbbell specimen is stretched to 100% elongation and is held for ten seconds. The specimen is released and the length is immediately measured, as well as within ten seconds of the release. As the data in Table 1 is demonstrated, all the gloves have a deformation less than 10%, demonstrating that these gloves are form fitting gloves.
Another common characteristic is the fact that all of these gloves are thicker than 0.05 mm. On one hand, it is required by FDA regulations and ASTM standards for medical devices. On the other hand technically, it is also extremely difficult, if not impossible to dip films at thickness less than 0.05 mm without compromising film integrity severely.
Dipped gloves are mainly used as medical devices as well as commonly seen in food service industries. However, the majority of food service gloves are made via a cutting and sealing process. The prior art cutting and sealing process would utilize polymers extruded by, but not limited to, blowing, casting or calendaring the polymers into thin films. Two films would be laid upon each other on a flat surface. If a glove is to be produced, a metallic hand shaped knife constructed from, but not limited to, copper or stainless steel would be applied to the top of the first film to cut through both film layers. Since the hand shaped knife is also heated, the layers would be welded together along the cutting line as the films are cut to form one glove.
Table 2 illustrates the properties of a typical prior art food service glove manufactured by polyethylene (PE) using the cutting and sealing method.
TABLE 2Typical properties of cut and sealed PE food service glovePropertiesPETensile Strength (MPa)11~15Elongation (%)~600Deformation after 100% stretch (%)30~50Thickness range (mm)0.01~0.02Weight (grams) <2
Disposable gloves used in the food service industry are generally manufactured using this process. The most common material for this process is polyethylene. Due to the combination of producing the gloves using a two dimensional flat former and the plastic nature of polyethylene, in contradistinction to the gloves formed by the dipping process, the gloves produced by the cutting and sealing process are much less form fitting to the user's hand. As a matter of fact, these gloves are very baggy and clumsy for task performance. In terms of deformation after a 100% stretch of the produced gloves, in contrast to the 10% recovery of the materials generally used in the dipping process, the use of polyethylene would exhibit a deformation of 30%, or even 50%. Furthermore, since these gloves could have a thickness of less than 0.02 mm, the durability of these gloves is poor. Technically, to exclude thicker films is not a problem, but such a thick polyethylene glove would be very uncomfortable to wear and would be difficult to perform the required tasks needed in the food handling industry.